2024 Ontario Grain Corn Ear Mould and Deoxynivalenol (DON) Mycotoxin Survey

OMAFA field crop specialists in collaboration with Grain Farmers of Ontario (GFO) and members of the Ontario Agri-Business Association (OABA) have completed the 2024 annual Ontario corn ear mould and DON mycotoxin survey. Corn ear moulds such as Gibberella and their corresponding mycotoxins occur every year in Ontario. These mycotoxins, particularly deoxynivalenol (DON, also referred to as vomitoxin) are produced primarily by Gibberella/Fusarium ear moulds and can be disruptive when fed to livestock, especially hogs. The 2024 survey found 94% of samples tested low (below 2.00 parts per million (ppm)) for DON and is one of the lowest DON level years compared to the 10-year average (86% of samples below 2.00 ppm).  


Methods

From September 23 to October 3, 2024, 261 ear corn samples were collected from across the province. Five consecutive ears were collected from four random locations (20 ears total) throughout a field and placed into high temperature driers (80°C) as soon as possible after collection. Pictures were taken to document moulds, insect/bird feeding damage and any other disorders (Figure 1). Dry ears were shelled and coarse ground and mixed for sub-sampling consistency. Sub samples were collected and finely ground for DON analysis by quantitative ELISA analysis at the University of Guelph Ridgetown Campus mycotoxin lab (ELISA is an enzyme-linked immunoassay laboratory test to detect quantities of substances).

Figure 1. Some common corn ear moulds which can be observed in Ontario.


Results

Results for the 2024 survey are presented in Table 1. Visual mould and DON concentrations were lower than long term survey averages (Table 2). While ear moulds were certainly evident in some samples, many displayed no symptoms, and no samples in the 2024 survey tested over 5 ppm. There may have been slightly more insect feeding damage in the 2024 survey than other recent years. These samples may have been associated with greater visual ear moulds, but given the lower pressure overall in 2024, DON levels are still relatively low. 

Table 1. Deoxynivalenol (DON) results from the 2024 Ontario grain corn ear mould and DON survey.

DON Concentration 
parts per million (ppm)
Samples
Total Samples261
< 0.50 ppm76%
0.50 to <2.00 ppm18%
2.00 to <5.00 ppm6%
5.00 ppm and greater0%

Table 2. DON results from the past ten years of Ontario grain corn ear mould and DON surveys.

DON (ppm)2015201620172018201920202021202220232024
< 0.50 75%48%69%33%84%58%63%88%41%76%
0.50 to <2.0020%26%17%27%12%31%26%10%36%18%
2.00 to <5.005%18%8%15%4%10%10%2%18%6%
5.00 and greater0%8%6%25%0%0%1%1%5%0%

Figure 2. Corn ear mould and deoxynivalenol (DON) survey sampling locations and results in 2024.

Distribution of samples and their corresponding DON levels are presented in Figure 2. Even with 94% of 2024 samples testing below 2 ppm, growers should be still be vigilant, as they may have individual fields with elevated DON. Fields should be evaluated for risk and consider harvesting and drying higher risk fields before infections worsen, and understand management and storage options for corn with higher DON concentrations (see “Going Forward” below). Ear moulds and mycotoxins occur every year in Ontario and fields need to be assessed individually.  


Growing Season

Unsettled weather and highly variable planting progress dominated spring of 2024. Frequent rains through April limited early corn planting. Frequent and spotty rains continued through most of May. During the first week of May, planting was generally limited to well drained soils in areas not receiving rain. Planting continued where possible. By the end of the second full week of May (May 18), planting progress was still highly variable with some areas nearing completion while others had barely started; some estimated around half of the Ontario corn crop may have been planted by this date. Planting slowly wrapped up over the last two weeks of May, with exception of some heavier textured soils where planting continued into June.

Earlier planted corn was starting to emerge the week of May 20 and had rapid growth with warm temperatures. Unsettled weather continued through June. While temperatures and heat units were generally greater than normal, there were also several short periods of very cool weather.

Frequent and in some cases intense (thunderstorm) rainfall continued through much of July. Some of the earliest corn fields started tasseling the third week of July while the following week (July 21) was likely the peak for tasseling and pollination across much of the province. Pollination continued after this window for later planted fields. Wet conditions during silking was a concern as ear moulds, like Gibberella Ear Rot, can establish on fresh green corn silks under wet conditions.

After the first full week of August, sunny and dry weather dominated across much of the province through to the last week of September. Very warm temperatures for a couple weeks in mid-September likely hastened corn crop maturity and the start of dry down.


Feeding Damage

Ear feeding by pests, particularly western bean cutworm (WBC), corn earworm (CEW) or birds can open husks and damage kernels which present opportunities for greater ear mould infection and DON. While still only representing a minority of samples, feeding damage appeared slightly more common in some areas than what has been observed in recent surveys. Peak WBC moth flights occurred the last two weeks in July, generally coinciding with tasseling in many areas. Where feeding damage was present, visual mould symptoms were usually more apparent.  


How to Sample Corn Loads

The importance of collecting representative samples cannot be emphasized enough. Significant variability in mycotoxin testing results can come from poor sampling.


Collecting a Bulk Sample from a Corn Load

While sampling from the top of a storage bin, truck or combine may be convenient, mycotoxins are rarely distributed evenly in grain loads, hence a sample probe is recommended. The more probes the better, but Ontario research shows that 4 probes sampling the full depth of wagons or trucks can do as good of a job representing corn loads as frequent tailgate sampling (swiping stream). Probes are not the major driver of variability experienced with DON testing. For moving grain streams, use a diverter or randomly collect cups of grain. Mix all collected probes/samples into one bulk sample of at least 2 kg.  


Collecting an Analysis Subsample from a Bulk Sample

Ontario research shows that one of the most significant sources of variability in DON testing comes from collecting the subsample for DON analysis (e.g. amount of the 2 kg bulk sample that is finely ground for the DON test). Individual kernels can be highly variable in DON and still coarse in size relative to the analysis subsample (e.g. a 200 g whole kernel sample used for fine-grinding may be representing the entire load with only 500 kernels). Therefore, the whole bulk sample should be ground (at least coarsely) and mixed so the analysis subsample contains parts of all kernels in the bulk sample. This subsample can then be ground finer to meet specifications of the DON test. More details on reducing sample variability through proper sampling and grinding is available HERE. Remember, samples must be processed quickly. It is important to ship or deliver fresh sample promptly, because the longer the sample sits around the greater potential for inaccurate results.


Going Forward

This survey does not capture all regions of the province and results can vary from field to field depending on local weather, hybrid, planting date, insect feeding, rotation, residue levels, fungicide practices and moisture. Results may not capture what is occurring in your field, therefore monitoring is always recommended.

Timely harvest is important. Leaving infected grain in the field allows ear rot fungi to continue growing, which increases risks of mouldy grain and mycotoxin contamination. Most ear rot fungi continue to grow (and potentially produce mycotoxins) until grain moisture is below 15%.  In high risk or severely infected fields, growers should consider harvesting at higher moisture and drying below 15%. 

If a field contains significant ear moulds (e.g. 10% or more ears with visual mould symptoms) collect a representative sample prior to harvest and test for mycotoxins before storing or feeding to livestock. A lab test is the only reliable way of determining mycotoxin levels. 

If possible, segregate contaminated corn separately. 

When ear rots are present, the following harvest, storage and feeding precautions are advisable (adapted from OMAFA Pub 811, Agronomy Guide for Field Crops):

• Harvest and dry as quickly as possible, especially susceptible hybrids. Mould and mycotoxin development ceases with grain moistures below 15%.

• If insect or bird damage is confined to certain areas, harvest and handle damaged rows separately.

• Cob, small kernels and fines typically have higher DON concentrations. Adjust harvest equipment to minimize grain damage and to remove insect damaged, infected or smaller tip kernels. Removing these parts when possible can be beneficial, though large amounts of removal may be required to significantly change grain concentrations.

• Clean bins before storing new grain and cool grain after drying. If possible, segregate corn by DON content to help match end use.

• Check stored grain often for temperature, wet spots, insects and mould. For grain with elevated mould content, market as soon as possible. Avoid long term storage.

• Exercise caution handling or feeding mouldy corn to livestock, especially hog breeding herds and weanling pigs. Pink or reddish moulds are particularly harmful. Test suspect samples for toxins. Work with a nutritionist to manage DON levels in feed.

• Agriculture and Agri-Food Canada guidelines for DON in animal feeds are:

  • pigs, calves, lambs, lactating cows, and lactating ewes, 1 part per million (ppm) in the diet
  • adult cattle, adult sheep, and poultry, 5 ppm in the diet


Considerations for 2025 corn crop

Preventing ear rots and mould can be difficult since weather is critical to development. A few things to consider for 2025. Hybrid selection is important, and while tolerant hybrids are available, none have complete resistance. Growers are encouraged to discuss ear mould tolerance with their seed supplier. The Ontario Corn Committee conducts DON hybrid trials for evaluating differences in DON susceptibility across Ontario hybrids (Figure 3). Reports are posted in the corn section of gocrops.ca. The 2023 DON hybrid trial report can be found HERE, while the 2024 report should be available in early 2025.

Figure 3. Hybrid table from the 2023 Ontario Corn Committee DON hybrid trial report available at gocrops.ca.

Crop rotation may help reduce ear rots. While certain foliar fungicides are also registered for suppressing ear rots, they need to be applied at VT/R1 when silks are green. See Ontario Crop Protection Hub HERE for fungicides labelled to suppress ear moulds. Cultural practices such as tillage are shown to have limited success in preventing ear and kernel rots.

Agricorp customers with mould issues are encouraged to immediately contact Agricorp at 1-888-247-4999 and report damage.


Additional Resources

For additional information, see the Crop Protection Network’s “Corn Management Disease Series – Ear Rots” publications at CropProtectionNetwork.org

CPN-2001 – Corn – An Overview of Ear-Rots

CPN-2002 – Corn – Mycotoxin FAQs

CPN-2003 – Corn – Grain Sampling and Mycotoxin Testing

CPN-2004 – Corn – Storing Mycotoxin-Affected Grain

Additional articles on managing corn ear moulds and mycotoxins are also available at FieldCropNews.com.

DON in Corn Silage

Harvest Tips for Mouldy Corn

Laboratories Offering Mycotoxin Analysis in Ontario

Good Mycotoxin Test Begins with a “Representative” Sample

Reducing DON Variability in Testing Truckloads of Corn – Prototype Grinder

End Uses for Mouldy Corn

To Clean or Not to Clean? Managing DON in Grain Corn

Fall Storage Tips for Mouldy Corn

Destroying a Corn Crop at Harvest Time

Land Application of Crops and By-products with Elevated DON Levels

Spring Storage Tips for Mouldy Corn


Acknowledgements

Sincere thanks to those who assisted in co-ordination and collection of samples: Agris Co-operative, Alliance Agri-Turf, Anderson Agronomy Services, Belmont Farm Supply, Benjamins Agronomy Services, Bruch Consulting, Central Ontario FS, Clark Agri Service, Grain Farmers of Ontario, Harriston Agromart, Hoegy’s Farm Supply, Holmes Agro, Lakeside Grain and Feed, MacEwen Agricentre Inc., Maizex Seeds, Midwest Co-op, Millstone Crop Services, Oxford Agropro Ltd., Parrish and Heimbecker, P.T. Sullivan Agro Inc., St. Lawrence Grain and Farm Supply, Sylvite Agri-Services Ltd., Syngenta, TCO Agromart, The Andersons Canada Ltd., Trouw Nutrition, Wellburn Agromart and the many producers and OMAFA staff also involved. This co-operation is critical for covering as much of the corn growing areas of the province as possible in a short period of time.

Thanks to Grain Farmers of Ontario, University of Guelph Ridgetown Campus mycotoxin lab and OMAFA for support of the survey as well as Ontario Agri-Business Association (OABA) and its members for their interest and participation.

This project was funded in part by the Sustainable Canadian Agricultural Partnership, a five-year federal-provincial-territorial initiative. 

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